In the related art, there is known a vehicle seat having a seat frame that is formed to have a closed cross sectional shape with a uniform horizontal cross sectional shape through aluminum extrusion molding (see, for example, JP-A-2015-101286). The seat frame having a closed cross sectional shape is provided with weight reduction holes by which the cross sectional shape of the seat frame is locally open. This structure aims to optimize balance between structural strength and weight.
However, even the closed cross sectional seat frame provided with weight reduction holes at a portion thereof as in the related art, has no change in external dimension as a seat frame, thereby not providing a space saving effect.